This invention relates generally to pneumatic block valves and more particularly to a multiport valve designed for use with gas centrifuges. One type of gas centrifuge with which this invention can be used is described in U.S. Pat. No. 3,946,942, issued to Gorden R. Theurich on Mar. 30, 1976, and incorporated herein by reference.
A proposed facility for the large-scale separation of uranium isotopes utilizes tens of thousands of gas centrifuges which are interconnected as a separation cascade. The cascade is designed to receive a feed stream of process gas (UF.sub.6) and to separate the same into a product stream enriched in the uranium-235 isotope and a waste stream depleted in that isotope. The interior of the typical cascade centrifuge is connected to three lines for the admission and withdrawal of process gas. These are a feed line for introducing UF.sub.6 to the centrifuge; a product line for removing enriched UF.sub.6 therefrom; and a waste line for removing depleted UF.sub.6 therefrom. Valves must be provided in each of these lines to isolate the centrifuge if it fails mechanically. In the event of such failure, these valves are actuated immediately to isolate the failed centrifuge from the remainder of the cascade. Without such isolation, the failure might generate pressure surges which could propagate throughout the cascade UF.sub.6 piping and cause catastrophic failure of other centrifuges. The typical centrifuge also is provided with a normally closed UF.sub.6 -bypass valve: in the event the centrifuge is isolated as described, this valve is opened to interconnect the isolated feed and product lines, thus placing the isolated machine on UF.sub.6 recycle.
A previous system for isolating and bypassing a gas centrifuge included four separate, individually actuated pneumatic valves. Three of these valves were connected respectively in the above-mentioned UF.sub.6 lines to isolate the typical centrifuge; the other was connected between the product and feed lines, to bypass product as described. The typical separate isolation valve comprised a reciprocatable plug assembly including a helical spring. The plug assembly was affixed to a plunger individually associated therewith. Air pressure was applied to the plunger to maintain its plug assembly in the valve-open position and its spring in compression. Removal of the air pressure permitted the spring to drive its plug assembly to the closed position. The single bypass plug assembly, which included a spring and a plunger, was maintained in its normally closed position by its spring and was opened when air was applied to its plunger. A multiport solenoid valve was used to supply air to the respective actuators of the valves.
The above-described system was found to be undesirably complex, bulky and expensive. For example, the volume of air required to operate the various valves necessitated a relatively large and costly solenoid valve. Also, the system required numerous air lines and fittings. Furthermore, the system was costly.